Evaluation of Capnography in Nonintubated Emergency Department Patients with Respiratory Distress

Objective: To evaluate the ability of noninvasive capnographic measurement of end-tidal CO₂ tension (Petco₂) to predict artenal CO₂ tension (Paco₂) in nonintubated ED patients with respiratory distress Methods: A prospective, nonblind study was performed in a level I trauma centerkommunity teaching hospital ED. Participants included all nonintubated adult patients with respiratory distress requiring measurement of arterial blood gases (ABGs): 29 patients were enrolled Petco_z was measured with a capnography monitor. using both baseline tidal volumes and forced expiratory volumes. The bias between Petco_? values and simultaneous measurements of Paco₂ by ABG was assessed Results: Petco, measured with forced expiration, and Pace_? agreed well, with bias (i.e, average difference) = 044 ± 0.52 kPa (33 ± 3.9 torr). Petco₂ measured with the tidal volume breath produced an unacceptably high bias of 0.82 ± 0.70 kPa (6.1 ± 5.2 torr). Levels of agreement between Paco₂ and Petco₂ were similar for smokers and nonsmokers and for men and women. The arterial-end-tidal CO₂ tension (Pa-etco₂) difference was not related to Paco₂ Pa-etco₂ correlated with age (r = 0.473; p = 0.01), and was significantly higher in patients with pulmonary disease (132 ± 0S6 kPa; 99 ± 42 torr) than it was in those without pulmonary disease (0.46 ± 055 kPa, 3.5 ± 4.1 torr, p < 0.001). Conclusions: Noninvasive Petco_z monitoring may adequately predict Paco₂ in nonintubated ED patients with respiratory distress who, are able to produce a forced expiration. Petco₂ is less accurate for Paco₂ with tidal volume breathing and in patients with pulmonary disease